1. Field of the Invention
The present invention relates to a back frame in a seat back for a vehicle seat, and more particularly to an improved back frame which is connected to a cushion frame by means of a reclining adjuster.
2. Description of the Prior Art
Conventionally, a back frame of this type, as shown in FIG. 1 and designated by (A'), includes a lower end to which an upper bracket (b1) of a reclining adjuster (B) is fixed. In this figure, reference (a1) designates an upper cross member of the back frame (A') , (a2) stands for a lower cross member of the same, and (a3) represents a free hinge of the same rotatably mounted to a cushion frame (C).
With such structure, when an eccentric load of W is given to the back frame (A') on the free hinge (a3) side of its upper cross member (a1), a torsional moment in the shown F1 direction as well as a load in the illustrated F2 direction are applied to the lower cross member (a2) of the back frame (A'). For this reason, in such prior art device, it is necessary to increase the strength of both of materials of the back frame (A') and the upper bracket (b1) of the reclining adjuster (B) to be connected with this back frame, which provides a disadvantage in reducing the weight of the back frame.